Hard-wired local area networks (LANs) are well established as cable communication links between workstations, computers, and other equipment. The wires and cables interconnecting these devices become cumbersome when a large number of devices need to be connected. For example, in an office with a large number of terminals or workstations, space and/or ducting must be provided for the cabling. Adding or moving a workstation frequently requires cabling to be added or moved. Additionally, the cabling may produce electromagnetic interference (EMI) and is susceptible to picking up EMI which may result in data errors.
In applications were the data is highly confidential, provisions must be made for confinement of the electric fields from the cable to prevent unauthorized interception of communication.
Radio frequency systems have been proposed as a means reducing or eliminating the interconnection cables. This solution requires the dedication of a portion of the radio frequency spectrum to the data communication channel. As the number of users increases and as the desired data transmission rate increases, the bandwidth of this channel must also increase. Different networks using the same frequency band must be geographically separated in order to avoid interference between the networks. One network that has been proposed would use a frequency bandwidth of 10 MHz in the 1700-1710 MHz frequency range. The proposed system could support up to 100 stations. The system is limited, however, to a single network within a 1000 foot radius zone.
Another solution which has been proposed is the use of diffuse infrared radiation. In this system, optical radiation from a transmitter is diffusely scattered from the surrounding walls, ceilings and other objects in the room effectively filling the entire room with the signal carrier. Receivers are non-directional and receive the incoming radiation over a wide field of view. The maximum data rate of such a system is limited by the dimensions of the room in which the system is operating because of the significant propagation times of reflected signals.
Another optical system which has been proposed uses transmitting and receiving optics which have a very small field of view on the order of one degree. These systems provide point-to-point communication and are capable of higher data rates than diffuse transmitting optical systems. These systems, however, require accurate alignment of the transmitting and receiving optics. Additionally, the construction of small angle receivers and transmitters poses problems.